Water-blown polyurethane foams contain many urea segments by the reaction between the isocyanate and water. Since the urea bond is less flexible than a polyurethane bond, the urea segments disadvantageously cause the foam to have a hard feel. Further, water tends to close the cells of the foam, which, in the case of slabstock foam, generally requires mechanical crushing to avoid puckering. By opening the cells of the foam with the lithium salts of the invention, one obtains a polyurethane flexible foam which is dimensionally stable and does not shrink either as a free rise or in the mold.
U.S. Pat. No. 3,108,975 describes the production of flexible polyurethane foams using certain basic compounds as catalysts without the need to employ amine-based catalysts. Described as catalysts were hydroxides of lithium, potassium, and sodium, with potassium and sodium emphasized and exemplified. Also mentioned were carboxylic acid salts of these metals, the carboxylic acids being predominately long chained but also including acetic and phthalic acid. The requirement for each of these compounds, however, is that they exhibit predominately basic activity and act as a source of hydroxide ions or anions to catalyze the reaction between isocyanate and polyol in a water-blown system. Thus, with an acetate group, the basic compound potassium acetate is exemplified; and with a water-based metal such as sodium, sodium hydroxide is exemplified. In the present invention, however, the lithium metal ion exhibits much weaker basic activity than sodium or potassium ions; and when combined with stronger short chain carboxylic acids having 1-6 carbon atoms, the lithium salts exhibit insufficient basic activity to act as catalyst substitutes for the above-described amine-based catalysts of U.S. Pat. No. 3,108,975.
U.S. Pat. No. 3,041,295 also describes the use of a lithium compound in flexible polyurethane water-blown foams but only in combination with a phosphate ester to prevent high temperature, high humidity breakdown of the foam. As in the previous patent, the lithium compound must exhibit basic activity; and exemplified are lithium carbonate, lithium hydroxide, and lithium ricinoleate. The lithium salts of the invention, however, are short chain carboxylic acid salts of lithium, which salts exhibit very weak basic, almost neutral, activity and are used as cell openers and aids in reduction of foam density.